Capsaicin creams, ointments, gels or lotions are well known in the art. Capsaicin is the pungent extract of peppers or chiles and, chemically, is trans-8-methyl-N-vanillyl-6-nonenamide. Capsaicin is believed to act on a subset of primary afferent nerves mostly of the c-fiber type. It binds to a receptor site at the nerve ending and therefore interferes with the binding of substance P. There are believed to be two phases of action, first excitation and then desensitization of the nerve to nociceptive impulses. The excitation results in the shot of hot peppers or a burning/tingling sensation when applied to the skin. The desensitization results from depletion of substance P and interference with afferent transmission in a nontetrodotoxin dependent manner. Clinically, the overall effect is pain relief.
Capsaicin can be readily obtained by the ethanol extraction of the fruit of capsicum frutescens or capsicum annum. It is available commercially from a variety of suppliers and can also be prepared synthetically by published methods. In some commercially available forms of capsaicin, a slightly different composition known as pseudocapsaicin is present. This pseudocapsaicin is pharmacologically indistinguishable from natural capsaicin. The present invention encompasses the use of both forms, and where the term capsaicin is used, both forms are meant.
Disclosures of capsaicin creams, ointments and gels and their operating mechanisms are disclosed in U.S. Pat. Nos. 4,997,853; 5,063,060; 5,178,879; 5,296,225 and 5,665,378.